2011-2015 is the Hottest 5-Year Period

In a new detailed analysis of the global climate between 2011 and 2015 – the hottest 5-year period on record – the UN World Meteorological Organization (WMO) has found an increasingly visible human footprint on extreme weather and climate events with dangerous and costly impacts.

The record temperatures were accompanied by rising sea levels and declines in Arctic sea-ice extent, continental glaciers and northern hemisphere snow cover.

This report confirms that the average temperature in 2015 had already reached the 1 degree-Celsius mark. Even that record is likely to be beaten in 2016.

Further in the report, WMO, the UN system’s authoritative voice on the state and behaviour of the Earth’s atmosphere, also highlighted some of the high-impact climate events.

These included the east African drought (2010-2012) that caused an estimated 258,000 deaths; the southern African drought (2013-2015); South-East Asia floods (2011) that killed 800 people and caused more than $40 billion in economic losses; heatwaves in India and Pakistan (2015) that claimed more than 4,100 lives; Hurricane Sandy (2012) which resulted $67 billion in economic losses in the United States; and Typhoon Haiyan (2013) which killed 7,800 people in the Philippines.

The five-year timescale allows for a better understanding of multi-year warming trends and extreme events such as prolonged droughts and recurrent heatwaves than an annual report.

The report further examined whether human-induced climate change was directly linked to individual extreme events.

Many individual extreme weather and climate events recorded during 2011-2015 were made more likely as a result of human-induced climate change. In the case of some extreme high temperatures, the probability increased by a factor of ten or more.

The WMO report was submitted to the Twenty-second Conference of the Parties of the UN Framework Convention on Climate Change (UNFCCC), known as COP 22, meeting Marrakech.

2011-2015 Weather: Hot and wild

Temperatures for the 2011-2015 period were 0.57 degree-Celsius (1.03 degree-Fahrenheit) above the average for the standard 1961-1990 reference period. The warmest year on record to date was 2015, with temperatures 0.76 degree-Celsius (1.37 degree-Fahrenheit) above the reference period.

Additionally global ocean temperatures also rose at unprecedented levels and sea-surface temperatures for the period were above average in most of the world, except in some parts of the Antarctic Ocean and the eastern South Pacific Ocean.

The period also saw a decline in the Arctic sea ice coverage. Averaged over 2011-2015, the mean Arctic sea-ice fell 28 per-cent below the 1981-2010 average. The minimum summer sea-ice extent of 3.39 million square-kilometres in 2012 was the lowest on record.

By contrast, for much of the period 2011– 2015, the Antarctic sea-ice extent was above the 1981-2010 mean value, particularly for the winter maximum.

Surface melting of the Greenland ice sheet also continued at above-average levels and mountain glaciers also continued their decline.

Northern hemisphere snow cover extent was well below average in all five years and in all months from May to August, continuing a strong downward trend.

Rising sea levels

Referring to studies, WMO said that the contribution of continental ice sheets, particularly in Greenland and west Antarctica, to sea-level rise is accelerating.

It noted on satellite record (from 1993 to present), sea levels have risen approximately 3 mm per year, based on tide gauges, compared to the average 1900-2010 trend of 1.7 mm per year.

As the oceans warm, they expand, resulting in both global and regional sea-level rise, adding that increased ocean heat content accounts for about 40 per cent of the observed global sea-level increase over the past 60 years.

Extreme Weather

The news release also mentions some examples of “extreme weather” which include record high seasonal and annual temperatures in the United States in 2012 and in Australia in 2013, hot summers in eastern Asia and western Europe in 2013, heatwaves in spring and autumn 2014 in Australia, record annual warmth in Europe in 2014, and a heatwave in Argentina in December 2013.

Pointing to a study of a 2014 drought in south-eastern Brazil that found that similar rainfall deficits had occurred on three other occasions since 1940, the impacts in 2014 were, however, exacerbated by a substantial increase in the demand for water, due to population growth. Such impacts show an increased link to human vulnerability.